A conventional arrangement of this type of clutch is illustrated in FIG. 3 (Published Patent Application (KOKAI) No. 57-79331).
In FIG. 3, 10 is a flywheel of an engine. A clutch disc 14 is sandwiched between the flywheel 10 and a pressure plate 12. The pressure plate 12 is covered by a clutch cover 16. A spring member 18, formed into an annular disc shape, and a release operation lever 20, transmitting a spring force of the spring member 18 go the pressure plate 12, are disposed at an outside of the clutch cover 16. The lever 20 is disposed at four places, for example, in a circumferential direction of the clutch with equal distances left therebetween and is so constructed than an inner peripheral side end of the lever 20 is pressed by a release bearing 24 concentric with an input shaft 22.
However, the conventional embodiment of FIG. 3 includes a problem that the spring member 18 is supported by an inner peripheral part of the clutch cover 16. The clutch cover 16 tends to be distorted by a reaction force of the spring member 18 to cause a decrease in a displacement of a tip end of the lever 20. The ratio of displacement of the pressure plate 2 to that of the lever 20, i.e. a release efficiency is deteriorated.
Furthermore, multiplication of the spring force of the spring member 18 is limited because a lever ratio of the lever 20 is small.
Furthermore, the axial dimension of the entire clutch becomes large because the spring member 18 and the lever 20 are disposed in series in an axial direction of the clutch.